V. K. Yanovskii

Superstructure formation and X-ray photoemission properties of the TlTiOPO4 surface

X-ray photoemission spectroscopy (XPS) measurements have been executed for TlTiOPO4 to elucidate the general features in the electronic structure of the KTiOPO4 family compounds. The peculiarities of the valence band structure have been discussed for the crystals. The persistence of core level binding energy differences O1s–P2p and O1s–Ti2p3/2 has been detected in TlTiOPO4 and KTiOPO4, which relates well with the constancy of averaged P–O and Ti–O chemical bond lengths in this crystal family. The superstructure ordering of the TlTiOPO4 surface subjected to polishing and annealing has been detected by reflectance high energy electron diffraction (RHEED). From comparison of surface crystallographic properties of TlTiOPO4 and KTiOPO4, the most typical superstructure indices have been revealed.

Electrical and nonlinear optical properties of KTiOPO4 single crystals doped by Nb or Sb

Single crystals of K1−xTi1−xNbxOPO4 and K1−xTi1−xSbxOPO4 solid solutions are grown and their dielectric properties, electrical conductivity, and nonlinear optical properties are studied. Maximal content of these dopants x is found to be 0.11 for Nb and 0.23 for Sb. This doping leads to the creation of the additional potassium vacancies and the high ionic conductivity σ33. Ferroelectric phase transitions become more diffuse and their temperature decreases. All the crystals show intensive broad maxima of the dielectric permeability attributed with the relaxation phenomena.

Oxygen-conducting crystals of La2Mo2O9: Growth and main properties

Single crystals of the anionic conductor La2Mo2O9 are grown by crystallization from a nonstoichiometric melt. Their polymorphism and domain structure, as well as the temperature dependences of conductivity and dielectric permittivity, are studied. In the temperature range 750–600°C, the conductivity of these crystals is as high as 10−1–10−2 Ω−1 cm−1.

Temperature dependences of the first critical field and critical current in the untwinned TmBa2Cu3Ox superconducting single crystals

Abstract The critical field Hc1 of the monodomain TmBa2Cu3Ox superconducting single crystals are measured along all three crystallographic axes. These data determine, in the logarithmic approximation, the ratio of the penetration depths λa:λb:λc = 1:1.7: 4.4 for T > 10K the dependence of Hc1 on the temperature is a linear function with a slope of about 22 Oe/K for H∥c and 3.1 Oe/K for H∥a. Angular dependences of the Meissner magnetic susceptibility and Hc1 in the (bc)-plane were studied. The expression derived in the ellipsoid approximation shows good agreement with these data. Temperature dependences of the critical current jc (T) are also measured. Different types of single crystals are used, including the monodomain crystal. For all samples the jc(T) curves follow the exponential dependence j c (T) = j c (0) exp (− T T 0 ) with a jc(0) value of about (2–3) × 106 A/cm2. The jc(0) independence on the density of domain walls suggests a weak pinning by a twinning plane.

Crystal growth and physical properties of Cs2Nb4O11 and Rb2Nb4O11 single crystals

The Cs 2 Nb 4 O 11 (CN) and Rb 2 Nb 4 O 11 (RN) single crystals are grown by means of flux method and their physical properties are studied. Despite the similarity of their chemical formulae the crystals are not isostructural. CN crystals undergo ferroelectric phase transition at 164 C. Both the compounds show electrical conductivity of about 10 -4 Ω -1 cm -1 at room temperature.

Structure and properties of niobium-doped potassium titanyl phosphate crystals

A series of potassium titanyl phosphate crystals, KTiOPO4, with various concentrations of niobium dopant has been grown, and some of their physical properties and structural characteristics have been studied. The incorporation of a small amount of niobium results in considerable changes in the electrical conductivity of KTP: Nb crystals and the temperature of the ferroelectric phase transition. Thus, the presence of 3–4 at. % of niobium results in an increase of conductivity by more than an order of magnitude, whereas TC decreases from 930 to 620°C. The X-ray diffraction study of the crystals has been performed at room temperature; the neutron diffraction analysis was made at temperatures of 20, 330, and 730°C. It was revealed that two crystallographically independent positions are statistically (by 90%) occupied by potassium cations, which results in the concentration of potassium atoms in the structure higher than it was expected from the condition of preservation of crystal electroneutrality. At high niobium concentrations, the monoclinic compound of the composition K2TiNb2P2O3 is formed.

The relaxation of the monodomain TmBa2Cu3Ox single crystal magnetization in the superconducting state

Abstract Measurements of the remanent magnetization relaxation RM ( t ) in the monodomain TmBa 2 Cu 3 O x single crystal are reported. The relaxation rate r ( T ) = d RM ( T , t )/d(ln t ) has a sharp maximum at temperature T = T max . The T max value is about 15 K for H = 2.8 kOe and it strongly depends on the magnitude of the applied magnetic field being shifted to higher temperatures as H is decreased. The normalized rate r ( T )/ RM 0 in contrast to the r ( T ) behavior, is almost isotropic irrespective of the H direction. The r ( T ) maximum is qualitatively reproduced by the calculation taking into account the thermal activated flux creep and Abrikosov vortices distribution according to the Bean model.

Observation of surface Mandelstamm-Brillouin light scattering spectra in high-temperature superconducting YBa2Cu3O7-° and La2-xSrxCuO4-δ single crystals and surface wave velocity determination

Abstract Observations of light scattering spectra caused by thermally excited surface Rayleigh waves in YBa2Cu3O7-δ and La2-xSrxCuO4-δ high Tc superconducting single crystals are reported. Surface wave velocities are obtained from the Brillouin line frequency shifts at room temperature.

Electrical and nonlinear optical properties of KTiOPO4 single crystals doped with niobium, antimony, and tantalum

Single crystals of K1 − xTi1 − xNbxOPO4 (KTP: Nb), K1 − xTi1 − xSbxOPO4 (KTP: Sb), and K1 − xTi1 − xTaxOPO4 (KTP: Ta) solid solutions are grown and their dielectric, conducting, and nonlinear optical properties are investigated. The maximum contents x of niobium, antimony, and tantalum impurities in the crystals are equal to 0.11, 0.23, and 0.25, respectively. The doping of the KTiOPO4 crystals with niobium, antimony, and tantalum brings about the formation of additional potassium vacancies and additional potassium positions and, as a consequence, an increase in the ionic conductivity σ33. An increase in the doping level leads to a smearing of the ferroelectric phase transitions and a decrease in the phase transition temperatures. The permittivity of the doped crystals exhibits a broad relaxation peak in the temperature range 200–600°C.

Structure and properties of antimony-doped potassium titanyl phosphate single crystals

Antimony-doped potassium titanyl phosphate (KTP) crystals of the composition KTiOPO4 are studied by X-ray diffraction analysis. It is shown that, with an increase of antimony content in KTP crystals, the occupancies of potassium positions change and new additional positions for potassium atoms arise. The formation of additional vacancies and splitting of the potassium-cation positions explain the considerable decrease in the temperature of the ferroelectric phase transition, enhancement of the relaxation phenomena, and an increase in electric conductivity of antimony-doped KTP crystals. Substitution of antimony atoms for titanium is accompanied by elongation of short and shortening of long Ti-O bonds in the TiO6 octahedra, processes which result in lower intensity of second-harmonic generation in laser-irradiated KTP crystals.